Although the focus of this study is on age-related macular degeneration, due to resource constraints, it took many years to recruit a sample of sufficient size to be able to address the original study aims. In the interim, analysis of refractive data, collected as part of the eye examination and within the parameters of the informed consent, were analyzed. Refractive error is a common ocular condition in the US and without correction, the vision in an affected eye is impaired. The most prevalent refractive error, myopia or nearsightedness, is increasing in frequency in many parts of the world. Although a genetic predisposition is believed to predispose individuals to develop myopia, other environmental factors such as near work activities are also thought to influence susceptibility. The Old Order Amish have an unique, largely agrarian lifestyle, avoid modern technology, and discontinue all formal schooling after the eighth grade. Because their environmental exposures are internally homogenous and do not entail much near work activity, we decided to investigate the distribution of refractive error, specifically myopia and hyperopia (farsightedness) within Amish sibships who are participants in this cohort study. We found that rates of myopia and hyperopia in the Old Order Amish siblings are lower than those observed in other population groups of similar age structure. Myopia and hyperopia were also observed to aggregate within sibships. Genetic factors are estimated to account for 70% of the variability in refractive error in these Amish sibships. The statistical analysis of data from families is complex because families are of different sizes and vary in composition. A subset of data from this Amish study served to demonstrate the application of a novel statistical method useful for analysis of family data. For more information, see http://biostats.bepress.com/upennbiostat/papers/art33. Recruitment for this study was completed in October 2011. The study has since ended. Study samples and data are being held in storage pending the availability of funds for their analysis.